An electric motor in the related art includes a sensor magnet and a cover member fixed to an end of a rotation shaft and covering at least a part of the end. The cover member has a holder located outside of an end face at the end of the rotation shaft. The holder includes a space portion with a non-circular cross section that extends in a direction of an axis of rotation of the rotation shaft. An outer shape of the sensor magnet is of a non-circular shape formed so as to conform to the sectional shape of the space portion. Hence, rotations of the sensor magnet about the axis of rotation are regulated by inserting the sensor magnet into the space portion (as is described, for example, in PTL 1).
In another electric motor in the related art, an end of the rotation shaft is of a non-circular shape having at least one planar portion and the sensor magnet is provided with an attachment hole of a non-circular shape same as the non-circular shape of the end of the rotation shaft. The sensor magnet is mounted to the rotation shaft by loose-fitting. Herein, rattling in the mount portions is suppressed by inclining the sensor magnet with respect to the rotation shaft until a part of the sensor magnet makes contact with the rotation shaft (as is described, for example, in PTL 2).